Lights flash when braking

Haven't driven my '74 hardly any at night until saturday. Everytime I stepped on the brake pedal, the lights would flash/blink once. From normal to dim back to normal. Just a split second flash. The ammeter needle didn't budge. My tach is also acting up. At idle or driving, the needle bouncing. At idle 800rpm, the needle goes up to around 2500 and back down. Driving at 2500rpm, it will go up to 5000. Associated or 2 seperate issues?

you have a grounding issue going on..most likely in the brake circuit...start by checking all the bulbs sockets for corrosion/bad connection..then move your way up through the brake wiring ground connections....check the brake switch ground wire continuity also...

Sounds like you have you have a short in the brake light circuit..

Just my $0.02..